Origin and Neoholocene evolution of spring-fed fens in Wardzyń, Łódź Upland, central Poland

Spring-fed fens in Wardzyń represent the rare group of alkaline mires supplied by artesian groundwater. Using multidisciplinary methods (including sedimentological, hydrometric and hydrochemical, pollen, macrofossil, malacological, geochemical, radiocarbon dating, and stable oxygen and carbon isotope analyses) we have been able to (1) reconstruct the main phases of spring-fed fen development, and to (2) determine the cause of Neoholocene groundwater ascension responsible for the mire inception. These phases are characterized by cyclic organic (peat) and carbonate (tufa) sedimentation associated with the Holocene fluctuations in humidity and temperature. The beginning of the activation of hydrological systems (involving the flow of confined groundwater of the Cretaceous aquifer) at Wardzyń occurred in the Subboreal period of the Holocene, after a long episode of decreased humidity initiated ca. 4.2 ka cal BP.